Photo-sensitive element and liquid crystal display with the same

ABSTRACT

A photo-sensitive element, a readout pixel with the photo-sensitive element, and a liquid crystal display with the readout pixels are described. The photo-sensitive element includes a switch TFT and a photo detecting device. The hate electrode of the switch TFT is electrically connected to a switch line and the source electrode of the switch TFT is electrically connected to a readout line. The photo detecting device is connected between the switch line and the drain electrode of the switch TFT for detecting the brightness of a light incident thereon. The photo detecting device is preferably a photo TFT, a photo diode, or a light sensitive resistor. The photo TFT and the switch TFT are preferably amorphous silicon transistors. The switch line is preferably a gate line disposed on the TFT array substrate of the crystal display.

FIELD OF THE INVENTION

The present invention generally relates to a photo-sensitive element.More particularly, the present invention relates to a photo-sensitiveelement having a detecting function and a liquid crystal display withthe same.

BACKGROUND OF THE INVENTION

Normally, a touch panel with a transparent surface is mounted on adisplay device, such as the liquid crystal display of a notebookcomputer or a personal digital assistant (PDA), which serves as an inputdevice or an input interface by a user without an additional keyboard ormouse. The touch panel has been used for a graphic process such as CAD.The touch panel is referred to as a touch film, a touch screen, adigitizer, a tablet or an electric graphic input panel (EGIP).

Depending upon the sensing method of a touch panel when a user touchesits surface, touch panels are usually classified as either a resistivetype, a capacitive type, or an electromagnetic type. In the resistivetype touch panel, a current change is detected according to the positionof a touching point by applying a DC voltage. Meanwhile, in thecapacitive type touch panel, the position of a touching point isdetected by a capacitance coupling with applying an AC voltage. Also, inthe electromagnetic type touch panel, the position of a touching pointis detected by detecting a resonant frequency resonated as an inductionvoltage by applying an electromagnetic field.

The respective type touch panels have different signal-amplifications,resolutions, designs and processing technology characteristics, so thatthe touch panel type is selected according to the desired use of thedisplay device using the touch panel and by considering the economicalefficiency, endurance and electro-optics, electrical, mechanical,environment-resisting, and input characteristics.

However, touch panels with a transparent surface mounted between theuser and the viewing surface of a display, such as a liquid crystaldisplay, have several drawbacks. For example, the transparent surface,together with other layers between the liquid crystal material mayresult in multiple reflections which decreases the contrast of thedisplay and produces glare. Moreover, externally adding a touch panel tothe display increases the manufacturing expense of the display andincreases the complexity of the display. Therefore, some of the liquidcrystal displays use and combine photo-sensitive elements on the TFTarray substrate of the liquid crystal display instead of employing atouch panel mounted on the top surface of the liquid crystal display sothat the assembly process of the liquid crystal display with a touchfunction is simplified.

Referring to FIG. 1A, a current type photo-sensitive element 100includes a photo thin film transistor 110 (photo TFT) and a switch thinfilm transistor 130 (switch TFT). The switch TFT 130 electricallyconnects to the readout line 140 with the source electrode 136 thereofand the switch line 150 with the gate electrode 132 thereof. The drainelectrode 134 thereof electrically connects to the source electrode 116of the photo TFT 110. In addition, the gate electrode 112 and the drainelectrode 114 both electrically connect to a bias voltage line 120. Thebias voltage line 120 provides a voltage to the photo TFT 110 so thatthe photo current of the photo TFT 110 is adjusted by the brightnesssensed by the photo TFT 110 while the switch TFT is turned on. Normally,the photo current is proportional to the brightness sensed by the photoTFT 110. However, there are so many metal lines, such as the readoutline 140, the switch line 150 and the bias line 120, are formed in theTFT array substrate so that the aperture ratio of the liquid crystaldisplay is reduced.

The current type photo-sensitive element 100 has to connect to at leastthree metal lines, such as the switch line, bias line and readout line,for driving the photo-sensitive element 100 to measure the brightnessthereon. Thus, the current type photo-sensitive element is also referredto a three-terminal type element. Referring to FIG. 1B, a charge typephoto-sensitive element 800 is described. The photo-sensitive element800 includes a photo thin film transistor 850 (photo TFT), a switch thinfilm transistor 840 (switch TFT), and a capacitor 860. The switch TFT840 electrically connects to the readout line 810 with the sourceelectrode thereof and the switch line 820 with the gate electrodethereof. The drain electrode thereof electrically connects to the sourceelectrode of the photo TFT 850. In addition, the gate electrode and thedrain electrode of the photo TFT 850 both electrically connect to a biasvoltage line 830. It is noted that the discharge type photo sensitiveelement is also referred to a three-terminal type element and differingfrom the current type photo sensitive element 100, the charge typephoto-sensitive element 800 has a additional element, the capacitor 860.

With the same manner, the charge type photo-sensitive element 800 alsohas to connect to at least three metal lines, such as the switch line,bias line and readout line, for driving the photo-sensitive element 800to measure the brightness thereon.

Therefore, the liquid crystal display combining photo-sensitive elementson the TFT array substrate results in more metal lines in the liquidcrystal display reducing the aperture ratio thereof. Accordingly, thereis a need to provide a high sensitive touch panel in the liquid crystaldisplay but not to significantly reduce aperture ratio thereof.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a liquid crystaldisplay with photo-sensitive elements on the thin film transistor arraysubstrate.

It is another objective of the present invention to providephoto-sensitive elements formed on the thin film transistor arraysubstrate with less metal lines thereon so as to not significantlyreduce aperture ratio of a liquid crystal display.

It is further another objective of the present invention to providephoto-sensitive elements formed on a thin film transistor arraysubstrate with higher sensitivity on the brightness variation.

It is yet another objective of the present invention to provide aphoto-sensitive element having a high photo sensitivity and a structureof two terminal points.

To accomplish the above objectives, the present invention provides aphoto-sensitive element including a first conductive line, a secondconductive line, a switch thin film transistor (switch TFT) and a photodetecting device. The switch TFT includes a first gate electrode, afirst terminal electrode and a second terminal electrode. The first gateelectrode is electrically connected to the first conductive line and thefirst terminal electrode is electrically connected to the secondconductive line. In addition, the photo detecting device is electricallyconnected between the first conductive line and the second terminalelectrode to detect a light incident thereon.

For example, the first gate electrode of the switch TFT is electricallyconnected to a switch line, the first conductive line, disposed on athin film transistor array substrate of a liquid crystal display and thesource electrode, one of the terminal electrodes, of the switch TFT iselectrically connected to a readout line, the second conductive line.The photo detecting device is connected between the switch line and thedrain electrode, another one of terminal electrodes, of the switch TFTfor detecting the brightness of a light incident thereon. The photodetecting device is a photo thin film transistor (photo TFT), a photodiode, or a light sensitive resistor. In one embodiment, the photodetecting device is a photo TFT, the gate electrode and drain electrodeof the photo TFT are electrically connected to the switch line, and thesource electrode of the photo TFT is electrically connected to the drainelectrode of the switch TFT. In another embodiment, the gate electrodeof the photo TFT is electrically connected to the switch line, the drainelectrode of the photo TFT is electrically connected to a common linedisposed on the TFT array substrate of the liquid crystal display, andthe source electrode of the photo TFT is electrically connected to thedrain electrode of the switch TFT. In yet another embodiment, the gateelectrode of the photo TFT is electrically connected to a common linedisposed on the TFT array substrate of the liquid crystal display, thedrain electrode of the photo TFT is electrically connected to the switchline, and the source electrode of the photo TFT is electricallyconnected to the drain electrode of the switch TFT.

The photo TFT and the switch TFT are preferably amorphous silicontransistors. The switch line is preferably a gate line disposed on theTFT array substrate of the liquid crystal display.

Another aspect of the present invention is to provide a readout pixelfor a liquid crystal display. The readout pixel includes a pixel thinfilm transistor (pixel TFT) and a photo-sensitive element. The gateelectrode of the pixel TFT is electrically connected to one of gatelines disposed on a thin film transistor array substrate of the liquidcrystal display and the photo-sensitive element further includes theforegoing switch thin film transistor (switch TFT) and the foregoingphoto detecting device. The gate electrode of the switch TFT iselectrically connected to one of the gate lines disposed on the thinfilm transistor array substrate and the source electrode of the switchTFT is electrically connected to a readout line. The photo detectingdevice is connected between the second gate line and the drain electrodeof the switch TFT for detecting the brightness of a light incidentthereon. In addition, the pixel TFT is also preferably an amorphoussilicon transistor.

Further another aspect of the present invention is to provide a liquidcrystal display. The liquid crystal display includes a color filtersubstrate (CF substrate), a thin film transistor array substrate (TFTsubstrate), and a layer of liquid crystal sandwiched between the CFsubstrate and the TFT substrate. In addition, a plurality of gate lines,data lines readout lines and readout pixels are disposed on the TFTsubstrate. Each readout pixel further includes the foregoing pixel TFTand the foregoing photo-sensitive element. The photo TFT, the switchTFT, and the pixel TFT are all preferably amorphous silicon transistors.In addition, the liquid crystal display may further include a readoutpixel storage capacitor provided between an electrode of the pixel TFTand the readout line for the readout pixel while a normal pixel storagecapacitor is provided between an electrode of a pixel TFT of the normalpixel and one of the gate lines adjacent to the normal pixel.

Because the amorphous silicon transistors are sensitive to lightincident thereon, the photo TFT according to the present invention canbe used as a basis upon which to detect the brightness of light incidentthereon. In addition, the photo TFT can also be replaced by a photodiode which is sensitive to light incident thereon and connected betweenthe switch TFT and the readout line. Alternatively, the photo TFT canalso be replaced by a light sensitive resistor which is also sensitiveto light incident thereon and connected between the switch TFT and thereadout line. Therefore, the photo detecting device, such as the photoTFT, the photo diode or the light sensitive resistor, can control thecurrent therethrough so that the light difference thereon can bemeasured in the liquid crystal display with readout pixels according tothe present invention.

Accordingly, the photo-sensitive element according to the presentinvention can only be connected between the readout line and the switchline to effectively reduce the complexity of the electrical circuit ofthe photo-sensitive element, and effectively enhance the currentdifference thereof for easily detecting the light incident thereon andalso enhance the aperture ratio of the liquid crystal display withreadout pixels. The photo-sensitive element can also use the switch lineto impose a higher voltage on the gate electrode or the drain electrodeof the photo TFT to increase the current difference thereof toeffectively measure the light incident thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention are more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1A illustrates a conventional current type photo-sensitive elementfor a liquid crystal display;

FIG. 1B illustrates a conventional charge type photo-sensitive elementfor a liquid crystal display;

FIG. 2 illustrates a first embodiment according to the presentinvention;

FIG. 3 illustrates the measured data curve of the first embodiment ofFIG. 2 at different environmental conditions;

FIG. 4A illustrates one readout pixel with the first embodiment of FIG.2 according to the present invention;

FIG. 4B illustrates another readout pixel with the first embodiment ofFIG. 2 according to the present invention;

FIG. 5A illustrates another readout pixel with the first embodiment of aliquid crystal display according to the present invention;

FIG. 5B illustrates a normal pixel of the liquid crystal displayaccording to the present invention;

FIG. 6 illustrates a second embodiment of a photo-sensitive elementsaccording to the present invention; and

FIG. 7 illustrates a third embodiment of a photo-sensitive elementsaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description is of the best presently contemplated mode ofcarrying out the present invention. This description is not to be takenin a limiting sense but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined by referencing the appended claims.

FIG. 2 illustrates a first embodiment of a photo-sensitive elementaccording to the present invention. The photo-sensitive element 200includes a switch TFT 210 and a photo TFT 220, each of the two TFTs hasa gate electrode and two terminal electrodes (source/drain electrodes)and the two TFTs are coupled between two conductive line, the switchline 230 and the readout line 240 The gate electrode 212 of the switchTFT 210 is connected to the switch line 230, and the gate electrode 222and the drain electrode 224 of the photo TFT 220 are also connected tothe switch line 230. The drain electrode 214 of the switch TFT 210 isconnected to the source electrode 226 of the photo TFT 220. In addition,the source electrode 216 of the switch TFT 210 is connected to thereadout line 240. The photo-sensitive element 200 is preferably acurrent type photo-sensitive element.

Comparing the photo-sensitive element 200 with the conventionalphoto-sensitive element 100 of FIG. 1A, the photo-sensitive element 200has no a bias voltage line any more through incorporating the biasvoltage line with the switch line 230, thus the photo-sensitive element200 does not have to be connected to a bias voltage line so that thequantity of the metal line in the TFT array substrate is reduced.Therefore, the photo-sensitive element 200 has to connect only theswitch line 230 and the readout line 240. Therefore, the bias voltageline is not necessary in the TFT array substrate. Particularly, only twometal lines have to be connected with the photo-sensitive element 200according to the present invention.

TABLE 1 The data of photo current W/L = 48/5 V_(D) = V_(G) = 5 V V_(D) =V_(G) = 10 V V_(D) = V_(G) = 15 V Dark 2.34E−08 9.38E−07 3.6E−06 Bright3.98E−07 2.43E−06 6.6E−06 I_(bright) − I_(dark) 3.75E−07 1.49E−063.01E−06  Unit: A where V_(D) is the voltage of the drain electrode ofthe photo TFT and V_(G) is the voltage of the gate electrode of thephoto TFT, and the bright environmental condition is under about 2150cd/m² and the dark environmental condition is in a black box isolatedfrom any light source.

In addition, table 1 shows the measured data of the photo current of thephoto-sensitive element 200. The data of the photo current in brightenvironmental conditions is measured at about 2150 cd/m² and the data ofthe photo current in dark environmental conditions is measured in ablack box isolated from any light source. Referring to table 1, thephoto current difference increases when the V_(G) and the V_(D)increases. Since the gate electrode 222 and the drain electrode 224 ofthe photo TFT 222 are both connected to the switch line 230, the switchline 230 can provide higher voltage for the photo TFT 220 compared tothe bias voltage of the conventional photo-sensitive element 100.Accordingly, the photo current difference of the present inventionbetween the dark environmental conditions and the bright environmentalcondition is larger than that of the conventional photo-sensitiveelement 100.

Referring to FIG. 3, the measured data curve of the first embodiment ofFIG. 2 at different environmental conditions is provided. The verticalaxis indicates the photo current and the horizontal axis indicates thevoltage difference between the source electrode and the drain electrodeof the switch TFT. The curve 310 is a drain current curve of the switchTFT measured in dark environmental conditions. The curve 320 is a loadcurve of the photo TFT measured in dark environmental conditions. Inaddition, the curve 330 is a load curve of the photo TFT measured inbright environmental conditions. The data of FIG. 3 is then summarizedto table 2. Table 2 is the current data of the photo TFT and the PhotoTFT+Switch TFT of the photo-sensitive element 200 according to thepresent invention.

TABLE 2 The current data of photo TFT and Photo TFT + Switch TFT W/L =48/5 Photo TFT Photo TFT + Switch TFT Dark 2.17E−06 8.28E−07 Bright2.93E−06 9.85E−07 I_(bright) − I_(dark) 7.64E−07 1.57E−07 Unit: A wherethe bright environmental condition is under about 2150 cd/m2 and thedark environmental condition is in a black box isolated from any lightsource.

In addition, table 3 is the current data of the photo TFT and the PhotoTFT+Switch TFT of the conventional photo-sensitive element 100.

TABLE 3 The current data of photo TFT and Photo TFT + Switch TFT of theconventional photo-sensitive element Photo TFT Photo TFT + Switch TFTDark 1.12E−09 1.10E−09 Bright 2.56E−08 2.41E−08 I_(bright) − I_(dark)2.45E−08 2.30E−08 Unit: A where the bright environmental condition isunder about 2150 cd/m² and the dark environmental condition is in ablack box isolated from any light source.

Comparing table 2 with table 3, the current difference between thebright and the dark environmental, I_(bright)−I_(dark), of the presentinvention is larger than that of the conventional photo-sensitiveelement about one order. Accordingly, the current difference of thephoto-sensitive element 200 can be easily detected by a readout circuitthat is connected to the readout line 240.

In addition, the photo element can be configured in every normal pixelor in some normal pixels to form the readout pixels so as to enable theTFT panel to have touch-read function also known as In-cell touch panel.The quantity of the photo elements configured in the TFT panel isdependent on the requested resolution of the touch-read function for theIn-cell touch panel.

Furthermore, FIG. 4A illustrates one readout pixel disposed on a thinfilm transistor array substrate (TFT substrate) of a liquid crystaldisplay with the first embodiment of FIG. 2 according to the presentinvention. Usually, the TFT substrate comprises a plurality of gatelines and data lines disposed thereon and the gate lines and the datalines together to define a plurality of pixels, however, for explanationsimply, FIG. 4A only shows a readout pixel which is respectively coupledto a gate line 420 and a data line 410, but not shows the normal pixelsat the same time. The readout pixel includes a pixel TFT 450 and aphoto-sensitive element 400. The pixel TFT 450 is used as the switchingelement to charge the pixel in the liquid crystal display. The drainelectrode and the gate electrode of the pixel TFT of the liquid crystaldisplay are connected to data line 410 and the gate line 420respectively. Furthermore, the photo-sensitive element 400 includes aphoto TFT 430 and a switch TFT 435 connected only between the gate line420 and the readout line 440. It is not necessary to lay out anadditional bias line in order to supply voltage to the photo TFT 430 andthe switch TFT 435 for driving photo current. Therefore, the apertureratio of the liquid crystal display with readout pixels according to thepresent invention is increased. In addition, the photo currentdifference of the present invention can be easily detected by thereadout circuit since the photo current difference is larger than thatof the conventional photo-sensitive element so that the size of thephoto-sensitive element can be reduced. Furthermore, the number of photoTFTs connected to each other for increasing the photo sensitivity isalso reduced.

FIG. 4B illustrates another readout pixel disposed on a thin filmtransistor array substrate of a liquid crystal display with the firstembodiment of FIG. 2 according to the present invention. The readoutpixel of FIG. 4B similar to the readout pixel of FIG. 4A. includes apixel TFT 450 a and a photo-sensitive element 400 a. However, thephoto-sensitive element 400 a is connected between the gate line 420 a,the same gate line connected to the gate electrode of the pixel TFT 450a, and the readout line 440. Accordingly, the pixel TFT and aphoto-sensitive element can be connected to the same gate line or adifferent gate line.

FIG. 5A illustrates another layout of a readout pixel based on the firstembodiment of a liquid crystal display according to the presentinvention. In the present invention, there are two kind pixels in theliquid crystal display which has the touch-read function, one is thereadout pixel with a photo element and the other is the normal pixelwithout the photo element. FIG. 5B illustrates a normal pixel without aphoto element of the liquid crystal display according to the presentinvention. The conventional photo-sensitive elements normally utilizethe common line as the bias line to provide the voltage to the photoTFT. However, between the readout line and the source electrode of thepixel TFT, a capacitance Cps is generated (not shown). Therefore, thestorage capacitor Cst of the normal pixel has to be increased tocompensate for the effect of the additional Cps in the readout pixel.Consequently, the aperture ratio of the liquid crystal display with thephoto-sensitive elements is limited.

In the first embodiment of the liquid crystal display with readoutpixels according to the present invention, the storage capacitor (Cst)552A of the readout pixel can be provided between the source electrodeof the pixel TFT 550A and the readout line 540, also referred to as Cston readout line. Furthermore, the storage capacitor (Cst) 552B of thenormal pixel can be provided between the source electrode of the pixelTFT 550B and the gate line 521, also referred to as Cst on gate.Therefore, the liquid crystal display with readout pixels according tothe present invention can effectively remove the common line from theTFT array substrate. The aperture ratio of the liquid crystal displaywith readout pixels according to the present invention is effectivelyincreased.

FIG. 6 illustrates a second embodiment of a photo-sensitive elementaccording to the present invention. The photo-sensitive element 600includes a switch TFT 610 and a photo TFT 620. The source electrode 616of the switch TFT 610 is connected to the readout line 640 and the gateelectrode 612 of the switch TFT 610 is connected to the switch line 630.The drain electrode 614 of the switch TFT 610 is connected to the sourceelectrode 626 of the photo TFT 620. The gate electrode 622 of the photoTFT 620 is connected to the switch line 630 and the drain electrode 624of the photo TFT is connected to a conductive line 650. While thephoto-sensitive element 600 is utilized insome or all of the pixels of aliquid crystal display, the switch line 630 can be corresponding to thegate line of the liquid crystal display and the conductive line 650 canbe corresponding to the common line of the liquid crystal display. Table4 is the current data of the photo TFT.

TABLE 4 The current data of photo TFT W/L = 48/5; V_(D) = 5 V V_(G) = 5V V_(G) = 10 V V_(G) = 15 V Dark 2.34E−08 7.88E−07 2.31E−06 Bright3.98E−07 1.85E−06 3.71E−06 I_(bright) − I_(dark) 3.75E−07 1.07E−06 1.4E−06 Unit: A where V_(D) is the voltage of the drain electrode ofthe photo TFT and V_(G) is the voltage of the gate electrode of thephoto TFT, and the bright environmental condition is under about 2150cd/m² and the dark environmental condition is in a black box isolatedfrom any light source.

The current difference, I_(bright)−I_(dark), is enhanced because thegate electrode 622 of photo TFT 620 is connected to the switch line 630which V_(G) is usually provided with higher voltage as compared to thatof the conventional photo-sensitive element 100 in a liquid crystaldisplay for driving on the photo current. The current difference islarge and easily detected by the readout circuit connected to thereadout line 640.

FIG. 7 illustrates a third embodiment of a photo-sensitive elementaccording to the present invention. The photo-sensitive element 700includes a switch TFT 710 and a photo TFT 720. The source electrode 716of the switch TFT 710 is connected to the readout line 740 and the gateelectrode 712 of the switch TFT 710 is connected to the switch line 730.The drain electrode 714 of the switch TFT 710 is connected to the sourceelectrode 726 of the photo TFT 720. The gate electrode 722 of the photoTFT 720 is connected to a conductive line 750 and the drain electrode724 of the photo TFT 720 is connected to the switch line 730. While thephoto-sensitive element 700 is utilized in some or all of the pixels ofa liquid crystal display, the switch line 730 can be corresponding tothe gate line of the liquid crystal display and the conductive line 750can be corresponding to the common line of the liquid crystal display.Table 5 is the current data of the photo TFT.

TABLE 5 The current data of photo TFT W/L = 48/5; V_(G) = 5 V_(D) = 5 VV_(D) = 10 V V_(D) = 15 V Dark 2.34E−08 2.81E−08 3.26E−08 Bright3.98E−07 4.72E−07 5.06E−07 I_(bright) − I_(dark) 3.75E−07 4.44E−074.74E−07 Unit: A where V_(D) is the voltage of the drain electrode ofthe photo TFT and V_(G) is the voltage of the gate electrode of thephoto TFT, and the bright environmental condition is under about 2150cd/m² and the dark environmental condition is in a black box isolatedfrom any light source.

The current difference, I_(bright)−I_(dark), is also enhanced becausethe drain electrode 724 of photo TFT 720 is connected to the switch line730 which V_(G) is provided higher voltage to the drain electrode 724 ofphoto TFT 720 as comparing to that of the conventional photo-sensitiveelement 100 for driving the photo current. The current difference islarge and easily detected by a readout circuit connected with thereadout line 740.

The pixel TFT, the switch TFT and the photo TFT according to the presentinvention are exemplarily constructed from amorphous silicontransistors. With the realization that amorphous silicon transistors aresensitive to light incident thereon, the photo TFT according to thepresent invention formed on the TFT array substrate may be used as abasis to detect the existence of or non-existence of ambient lightincident thereon (e.g., relative values thereto). The photo TFT can alsobe replaced by a photo diode which is sensitive to light incidentthereon and connected between the switch TFT and the switch line. Thatis, the photo-sensitive element may be constituted by a switch TFT and aphoto diode. Alternatively, the photo TFT can also be replaced by alight sensitive resistor which is also sensitive to light incidentthereon and connected between the switch TFT and the switch line.Therefore, the photo-sensitive element may also be constituted by aswitch TFT and a light sensitive resistor. Accordingly, thephoto-sensitive element can be constituted by a switch TFT and a photodetecting device, for example, a photo TFT, a photo diode or a lightsensitive resistor, to control the current therethrough so that thelight difference thereon can be detected in the liquid crystal displaywith readout pixels having the photo-sensitive element according to thepresent invention.

The photo-sensitive element according to the present invention can onlybe connected between the readout line and the switch line to effectivelyreduce the complexity of the electrical circuit of the photo-sensitiveelement, effectively enhance the current difference thereof to easilydetect the light incident thereon, and effectively increase the apertureratio of the liquid crystal display with readout pixels. Thephoto-sensitive element according to the present invention can also usethe switch line to impose a higher voltage on the gate electrode or thedrain electrode of the photo TFT to increase the current differencethereof for easily detecting the light incident thereon. Accordingly,the two terminal electrodes, the source electrodes and the drainelectrodes of the switch TFT and the photo TFT, are interchangeable inthe foregoing description and the following claim limitation.

As is understood by a person skilled in the art, the foregoing preferredembodiments of the present invention are illustrative of the presentinvention rather than limiting of the present invention. It is intendedthat various modifications and similar arrangements would be includedwithin the spirit and scope of the appended claims, the scope of whichshould be accorded the broadest interpretation so as to encompass allsuch modifications and similar structures.

1. A photo-sensitive element, comprising: a first conductive line; asecond conductive line; a switch thin film transistor (switch TFT)having a first gate electrode, a first terminal electrode and a secondterminal electrode, wherein said first gate electrode is electricallyconnected to said first conductive line and said first terminalelectrode is electrically connected to said second conductive line; anda photo thin film transistor (photo TFT) having a second gate electrode,a third terminal electrode and a fourth terminal electrode, wherein thephoto TFT is electrically connected between said first conductive lineand said second terminal electrode to detect a light incident thereon,the first gate electrode of the switch TFT and the second gate electrodeof the photo TFT are connected to each other, and the second terminalelectrode of the switch TFT and the third terminal electrode of thephoto TFT are connected to each other.
 2. The photo-sensitive element ofclaim 1, wherein said first conductive line and said second conductiveline are respectively a switch line and a readout line of said switchTFT.
 3. The photo-sensitive element of claim 1, wherein said firstterminal electrode and said second terminal electrode are respectivelysource/drain electrodes of said switch TFT.
 4. The photo-sensitiveelement of claim 1, wherein said third terminal electrode and saidfourth terminal electrode are respectively source/drain electrodes ofsaid photo TFT.
 5. The photo-sensitive element of claim 1, wherein saidphoto TFT is disposed on a substrate.
 6. The photo-sensitive element ofclaim 5, wherein said substrate is a TFT array substrate of a liquidcrystal display.
 7. The photo-sensitive element of claim 1, wherein saidsecond gate electrode and said fourth terminal electrode are bothelectrically connected to said first conductive line.
 8. Thephoto-sensitive element of claim 1, wherein said second gate electrodeis electrically connected to said first conductive line, said fourthterminal electrode is electrically connected to a third conductive line,and said third terminal electrode is electrically connected to saidsecond terminal electrode.
 9. The photo-sensitive element of claim 1,wherein said second gate electrode is electrically connected to a thirdconductive line, said fourth terminal electrode is electricallyconnected to said first conductive line, and said third terminalelectrode is electrically connected to said second terminal electrode.10. The photo-sensitive element of claim 1, wherein said photo TFT is anamorphous silicon transistor.
 11. The photo-sensitive element of claim1, wherein said switch TFT is an amorphous silicon transistor.
 12. Areadout pixel for a liquid crystal display, comprising: a pixel thinfilm transistor (pixel TFT) disposed on a thin film transistor arraysubstrate of said liquid crystal display; a photo-sensitive elementdisposed on said thin film transistor array substrate, wherein saidphoto-sensitive element further comprises: a first conductive line; asecond conductive line; a switch thin film transistor (switch TFT)having a first gate electrode, a first terminal electrode and a secondterminal electrode, wherein said first gate electrode is electricallyconnected to said first conductive line and said first terminalelectrode is electrically connected to said second conductive line; anda photo thin film transistor (photo TFT) having a second gate electrode,a third terminal electrode and a fourth terminal electrode, wherein thephoto TFT is electrically connected between said first conductive lineand said second terminal electrode to detect a light incident thereon,the first gate electrode of the switch TFT and the second gate electrodeof the photo TFT are connected to each other, and the second terminalelectrode of the switch TFT and the third terminal electrode of thephoto TFT are connected to each other.
 13. The readout pixel of claim12, wherein said pixel TFT has a third gate electrode electricallyconnected to a first gate line of said thin film transistor arraysubstrate, and said first conductive line is a second gate line of saidthin film transistor array substrate adjacent to said first gate line.14. The readout pixel of claim 12, wherein said pixel TFT has a thirdgate electrode electrically connected to said first conductive line, andsaid first conductive line is a gate line of said thin film transistorarray substrate.
 15. The readout pixel of claim 12, wherein said secondgate electrode and said fourth terminal electrode are both electricallyconnected to said first conductive line.
 16. The readout pixel of claim12, wherein said second gate electrode is electrically connected to saidfirst conductive line, said fourth terminal electrode is electricallyconnected to a third conductive line, and said third terminal electrodeis electrically connected to said second terminal electrode.
 17. Thereadout pixel of claim 16, wherein said third conductive line is acommon line of said thin film transistor array substrate.
 18. Thereadout pixel of claim 12, wherein said second gate electrode iselectrically connected to a third conductive line, said fourth terminalelectrode is electrically connected to said first conductive line, andsaid third terminal electrode is electrically connected to said secondterminal electrode.
 19. The readout pixel of claim 18, wherein saidthird conductive line is a common line of said thin film transistorarray substrate.
 20. The readout pixel of claim 12, wherein said photoTFT is an amorphous silicon transistor.
 21. The readout pixel of claim12, wherein said switch TFT and said pixel TFT are amorphous silicontransistors.